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I came here to say just that. This is a horrible idea and definitely not something you should do. Just use sealed AGM batteries, don't burn your house down or

I came here to say just that. This is a horrible idea and definitely not something you should do. Just use sealed AGM batteries, don't burn your house down or deal with spilling chemicals everywhere. Even just drawing in parallel from batteries like this is a fire hazard. Charging is an out of your mind goal.

agumonkey 10y ago
Wow, as someone uneducated about anything related to electricity and power, seeing the picture in the article really made me want to emulate the setup. Not anymore.
- gravypod 10y ago
  You joke buy many many people don't know how volatile battery chemistry is and how different charging of Lithium cells works. I'd not have known how much of a bad idea this was had I not been a long time fan of EEVBlog. It's an entirely different world when touching Lithium cells. Even drawing in parallel from cells from the same batch can be a bad idea.
userbinator 10y ago
Even just drawing in parallel from batteries like this is a fire hazard. I think you've confused parallel with series; in parallel, the batteries will naturally balance themselves to the same voltage and discharge proportionally to their capacity. It's the series configurations that are riskier and need extra balancing circuitry. Also, I'm pretty sure the bulk of fires are from the much more fragile pouch "lipo" cells, not hard-cased 18650s like these. You may note the extremely large number of lipo fire videos on YouTube as evidence. On the other hand, 18650s tend to be quite a lot more robust and difficult to ignite: https://www.youtube.com/watch?v=vi5lGtm_ItQ https://www.youtube.com/watch?v=vi5lGtm_ItQ https://www.youtube.com/watch?v=uoFRrmhXoVw https://www.youtube.com/watch?v=uoFRrmhXoVw
- qoobaa 10y ago
  I think @gravypod actually meant parallel connection, it might be quite dangerous in fact - you don't even need to draw anything from the battery to mess things up. If you connect a 100 cells in parallel and one cell dies creating a short in the circuit, the rest of cells will discharge through the shorted one. When you short a single 18650 cell, it outputs about 6-7 A of current on average. Multiplying by 100 gives you 600-700 A of current flowing through a single cell. That's why people use fuses to create parallel modules.
  - gravypod 10y ago
    Yes that was mentioned in one of the maaaany EEVBlog videos iv watch that these fail closed sometimes as well as the recommendation that "you should never buy lipo cells without a built-in controller" comeing from a guy far smarter then I about electronics design. If he is afraid of it, it's for a good reason.
    - throwaway7767 10y ago
      > Yes that was mentioned in one of the maaaany EEVBlog videos iv watch that these fail closed sometimes as well as the recommendation that "you should never buy lipo cells without a built-in controller" comeing from a guy far smarter then I about electronics design. If he is afraid of it, it's for a good reason. If you're building a large pack you don't want cells with a built-in protection. You connect all the cells to a pack-wide BMS that keeps things safe. The important thing is to never use unprotected cells without some protection circuit in the pack.

agumonkey 10y ago

Wow, as someone uneducated about anything related to electricity and power, seeing the picture in the article really made me want to emulate the setup. Not anymore.

gravypod 10y ago
You joke buy many many people don't know how volatile battery chemistry is and how different charging of Lithium cells works. I'd not have known how much of a bad idea this was had I not been a long time fan of EEVBlog. It's an entirely different world when touching Lithium cells. Even drawing in parallel from cells from the same batch can be a bad idea.

userbinator 10y ago

Even just drawing in parallel from batteries like this is a fire hazard. I think you've confused parallel with series; in parallel, the batteries will naturally balance themselves to the same voltage and discharge proportionally to their capacity. It's the series configurations that are riskier and need extra balancing circuitry. Also, I'm pretty sure the bulk of fires are from the much more fragile pouch "lipo" cells, not hard-cased 18650s like these. You may note the extremely large number of lipo fire videos on YouTube as evidence. On the other hand, 18650s tend to be quite a lot more robust and difficult to ignite: https://www.youtube.com/watch?v=vi5lGtm_ItQ https://www.youtube.com/watch?v=vi5lGtm_ItQ https://www.youtube.com/watch?v=uoFRrmhXoVw https://www.youtube.com/watch?v=uoFRrmhXoVw

qoobaa 10y ago
I think @gravypod actually meant parallel connection, it might be quite dangerous in fact - you don't even need to draw anything from the battery to mess things up. If you connect a 100 cells in parallel and one cell dies creating a short in the circuit, the rest of cells will discharge through the shorted one. When you short a single 18650 cell, it outputs about 6-7 A of current on average. Multiplying by 100 gives you 600-700 A of current flowing through a single cell. That's why people use fuses to create parallel modules.
- gravypod 10y ago
  Yes that was mentioned in one of the maaaany EEVBlog videos iv watch that these fail closed sometimes as well as the recommendation that "you should never buy lipo cells without a built-in controller" comeing from a guy far smarter then I about electronics design. If he is afraid of it, it's for a good reason.
  - throwaway7767 10y ago
    > Yes that was mentioned in one of the maaaany EEVBlog videos iv watch that these fail closed sometimes as well as the recommendation that "you should never buy lipo cells without a built-in controller" comeing from a guy far smarter then I about electronics design. If he is afraid of it, it's for a good reason. If you're building a large pack you don't want cells with a built-in protection. You connect all the cells to a pack-wide BMS that keeps things safe. The important thing is to never use unprotected cells without some protection circuit in the pack.